Coronary heart disease (CHD) is one of the major causes of morbidity and mortality worldwide. Despite attempts to modify risk factors such as obesity, smoking, lack of exercise, and treatment of dyslipidemia with dietary modification or drug therapy, CHD remains the most common cause of death in the U.S. Over 50% of all CHD deaths are due to underlying atherosclerotic coronary heart disease.
Dyslipidemia is a major risk factor for CHD. Low plasma levels of high density lipoprotein (HDL) cholesterol with either normal or elevated levels of low density (LDL) cholesterol is a significant risk factor for developing atherosclerosis and associated coronary artery disease in humans. Indeed, several studies on lipoprotein profiles of CHD patients have shown that about 50% of the CHD patients have cholesterol levels that are considered to be in the normal range (<200 mg/dl). Furthermore, these studies found low HDL cholesterol in about 40% of the normo-cholesterolemic CHD patients as compared to the general population reported in the National Health and Nutrition Examination Survey. Since low levels of HDL cholesterol increase the risk of atherosclerosis, methods for elevating plasma HDL cholesterol would be therapeutically beneficial for the treatment of cardiovascular disease including, but not limited to, atherosclerosis, CHD, stroke, and peripheral vascular disease.
Cholesterol ester transfer protein (CETP) is a 74 KD glycoprotein that facilitates the exchange of cholesterol esters in HDL for triglycerides in triglyceride-rich lipoproteins (A. R. Tall et. al., (1999) 1999 George Lyman Duss Memorial Lecture: Lipid transfer proteins, HDL metabolism and atherogenesis. Arterio. Thromb. Vasc. Biol. 20:1185-1188.). The net result of CETP activity is a lowering of HDL cholesterol and an increase in LDL cholesterol. This effect on lipoprotein profile is believed to be proatherogenic, especially in subjects whose lipid profile constitutes an increased risk for CHD. Niacin can significantly increase HDL, but has serious toleration issues that reduce compliance. Fibrates and the HMG CoA reductase inhibitors raise HDL cholesterol only modestly (˜10-12%). As a result, there is a significant unmet medical need for a well-tolerated agent that can significantly elevate plasma HDL levels, thereby reversing or slowing the progression of atherosclerosis.
CETP is expressed in multiple tissues and secreted into plasma, where it associates with HDL (X. C. Jiang et. al., (1991) Mammalian adipose tissue and muscle are major sources of lipid transfer protein mRNA. J. Biol. Chem. 266:4631-4639). Humans and monkeys, which express CETP, have relatively low HDL cholesterol, whereas mice and rats do not express CETP and carry nearly all their cholesterol in HDL. Further more, transgenic expression of CETP in mice results in significantly reduced HDL cholesterol levels and development of severe atherosclerosis compared to control mice (K. R. Marotti et. al., (1993) Severe atherosclerosis in transgenic mice expressing simian cholesteryl ester transfer protein. Nature:364, 73-75). Expression of human CETP in Dahl salt-sensitive hypertensive rats led to spontaneous combined hyperlipidemia, coronary heart disease and decreased survival (V. L. M. Herrera et. al., (1999) Spontaneous combined hyperlipidemia, coronary heart disease and decreased survival in Dahl salt-sensitive hypertensive rats transgenic for human cholesteryl ester transfer protein. Nature Medicine: 5, 1383-1389).
Antibodies either directly injected into the plasma or generated through vaccine injection can effectively inhibit CETP activity in hamsters and rabbits resulting in elevated HDL cholesterol (C. W. Rittershaus, (1999) Vaccine-induced antibodies inhibit CETP activity in vivo and reduce aortic lesions in a rabbit model of atherosclerosis. Furthermore, antibody neutralization of CETP in rabbits has been shown to be anti-atherogenic (Arterio. Thromb. Vasc. Biol. 20, 2106-2112; G. F. Evans et. al., (1994) Inhibition of cholesteryl ester transfer protein in normocholesterolennc and hypercholesterolemic hamsters: effects on HDL subspecies, quantity, and apolipoprotein distribution. J. Lipid Research. 35, 1634-1645). However, antibody and/or vaccine therapy is not currently a viable option for the treatment of large populations of patients in need of treatment for dyslipidemia and resultant or associated disease state manifestations.
Cholesterol ester transfer protein (CETP) catalyzes the exchange of neutral lipid between HDL and apoB-containing lipoprotein particles. As a net result of this exchange, HDL cholesterol is reduced and LDL particles are further enriched with cholesterol, resulting in LDL cholesterol elevation and formation of small dense LDL particles, which are believed to be more atherogenic. CETP inhibition (small molecule, antibody, anti-sense oligo etc.) effectively elevates HDL cholesterol and also reduces LDL cholesterol in animal models as well as in humans (Whitlock, M. et al., J. of Clin. Invest., 1989, Vol. 84, 129-137, Hirochi, O. et al., Nature, 2000, Vol. 406, 203-207, Grooth, G. et al., Circulation, 2002;105:2159-2165, Clark, R. et al., Arterioscler Thromb Vasc Biol. 2004;24:1-9, Brousseau M. et al., New Engl. J. Med., 2004, Vol. 350:1505-1515). Further, CETP inhibition leads to the formation of less-dense LDL particles-a benefit in addition to LDL cholesterol lowering (Brousseau M. et al., New Engl. J. Med., 2004, Vol. 350:1505-1515). Thus, administration of CETP inhibitors to humans in need thereof would significantly elevate HDL cholesterol level and reduce LDL cholesterol levels and increase LDL particle size, all of which are believed to benefit patients exposed to atherosclerotic risks.
There have been several reports of small molecule CETP inhibitors. Barrret et. al. (J. Am Chem. Soc., 188, 7863, (1996)) and Kuo et al. (J. Am. Chem. Soc., 117, 10629, (1995)) describe cyclopropan-containing CETP inhibitors. Pietzonka et al. (Biorg. Med. Chem. Lett. 6, 1951 (1996)) describe phosphanate-containing analogs as CETP inhibitors. Coval et al. (Bioorg. Med. Chem. Lett. 5, 605, (1995)) describe Wiedendiol-A and -B related sesquiterpines as CETP inhibitors. Japanese Patent Application No. 10287662-A describes polycyclic, non-amine containing, polyhydroxylic natural compounds possessing CETP inhibition properties. Lee et al. (J. Antibiotics, 49, 693-96 (1996)) describe CETP inhibitors derived from an insect fungus. Busch et al. (Lipids, 25, 216-220 (1990)) describe cholesteryl acetyl bromide as a CETP inhibitor. Morton and Zillversmit (J. Lipid Res., 35, 836-47 (1982)) describe that p-chloromercuriphenyl sulfonate, p-hydroxymercuribenzoate and ethyl mercurithiosalicylate inhibit CETP. Connolly et al. (Biochem. Biophys. Res. Comm. 223, 42-47 (1996)) describe other cysteine modification reagents as CETP inhibitors. Xia et al. Describe 1,3,5-triazines as CETP inhibitors (Bioorg. Med. Chem. Lett., 6, 919-22 (1996)). Bisgaier et al. (Lipids, 29, 811-8 (1994) describe 4-phenyl-5-tridecyl-4H-1,2,4-triazole-thiol as a CETP inhibitor. Oomura et al., disclose non-peptidic tetracyclic and hexacyclic phenols as CETP inhibitors in Japanese Patent Application No. 10287662.
U.S. Pat. No. 6,586,448 B1 describes 4-caboxamino-2-substituted-1,2,3,4-tetrahydroquinolines of formula I
and prodrugs thereof, and pharmaceutically acceptable salts of said compounds and said prodrugs; wherein R1, R2, R3, R4, R5, R6, R7 and R8 are as defined therein. Similarly, PCT patent applications WO 03/063868A1, WO 0017164, No.0017165, and WO 0017166, discloses variously, formulations, methods of preparation and methods of use of tetrahydroquinoline compounds generally related to that of U.S Pat. No. 6,586,448 B1 from which it derives or is a divisional application thereof.
European Patent Application No. 818448 by Schmidt et al. describes tetrahydroquinoline derivatives as cholesteryl ester transfer protein inhibitors. European Patent Application No. 818197, Schmek et al., describe pyridines with fused heterocycles as cholesteryl ester transfer protein inhibitors. Brandes et al. in German Patent Application No. 19627430 describe bicyclic condensed pyridine derivatives as cholesteryl ester transfer protein inhibitors. In U.S. Pat. No. 6,207,671 Schmidt et al., describe substituted pyridine compounds as CETP inhibitors. In WO Patent Application No. 09839299, and WO Patent application No.03028727 by Muller-gliemann et al. and Erfinder/Anmelder respectively, describe quinoline derivatives as cholesteryl ester transfer protein inhibitors.
The above disclosures notwithstanding, a great need remains for effective compounds useful as CETP inhibitors to treat conditions caused by, associated with or exacerbated by dyslipidemia.